U.S. patent number 5,506,786 [Application Number 08/285,871] was granted by the patent office on 1996-04-09 for cutting apparatus.
This patent grant is currently assigned to Konica Corporation. Invention is credited to Takayoshi Hashimoto, Masataka Inagi, Masao Itoh, Toyotsugu Itoh, Sunao Kawada.
United States Patent |
5,506,786 |
Itoh , et al. |
April 9, 1996 |
Cutting apparatus
Abstract
A cutting apparatus for finishing a surface of a substrate of a
photoreceptor drum of an image forming apparatus estimates a finish
state of the surface on real time with the finishing. The cutting
apparatus has a detector to detect a cutting force to a cutting
tool from the surface in finishing, a memory to store a cutting
force pattern to distinguish the finish state of the surface,
comparator means to compare the detected cutting force with the
stored cutting force pattern and judging means to judge the finish
state of the surface along with the progress of the cutting
process.
Inventors: |
Itoh; Masao (Hachioji,
JP), Inagi; Masataka (Hachioji, JP),
Kawada; Sunao (Hachioji, JP), Itoh; Toyotsugu
(Hachioji, JP), Hashimoto; Takayoshi (Hachioji,
JP) |
Assignee: |
Konica Corporation
(JP)
|
Family
ID: |
27465954 |
Appl.
No.: |
08/285,871 |
Filed: |
August 4, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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430286 |
Aug 14, 1992 |
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Foreign Application Priority Data
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Aug 26, 1991 [JP] |
|
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3-213679 |
Sep 24, 1991 [JP] |
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3-076552 U |
Sep 24, 1991 [JP] |
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3-243383 |
Sep 24, 1991 [JP] |
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3-243384 |
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Current U.S.
Class: |
700/175; 340/683;
702/8; 73/660 |
Current CPC
Class: |
B23B
1/00 (20130101); B23Q 11/0042 (20130101); B23Q
11/1084 (20130101); G05B 19/4163 (20130101) |
Current International
Class: |
B23Q
11/00 (20060101); B23Q 11/10 (20060101); B23B
1/00 (20060101); G05B 19/416 (20060101); G06F
017/18 () |
Field of
Search: |
;364/474.17,474.15,474.16,507,508,550,551.01 ;73/104,660
;318/565,569 ;409/80 ;340/679,683,825.23 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Envall, Jr.; Roy N.
Assistant Examiner: Oakes; Brian C.
Attorney, Agent or Firm: Bierman; Jordan B. Bierman and
Muserlian
Parent Case Text
This application is a continuation of application Ser. No.
07/930,286, filed Aug. 14, 1992, now abandoned.
Claims
What is claimed is:
1. A cutting apparatus for finishing a surface of a workpiece, said
workpiece comprising a metallic material to be used as a substrate
of a photoreceptor in an image forming apparatus, said cutting
apparatus comprising;
a cutting tool;
a detector contacting said cutting tool, for directly detecting a
cutting force exerted on said cutting tool by said workpiece, and
generating a force signal responsive to said cutting force;
a memory for storing a plurality of mode pattern data, said mode
pattern data including a plurality of mode patterns, each
expressing one of a plurality of types of defects which may occur
on said surface of said workpiece; wherein said mode pattern data
includes a plurality of limit values;
a determinator for determining a start time and an end time of a
cutting of said workpiece with said cutting tool, according to said
cutting force;
a comparator for performing a comparative analysis on said force
signal and said mode pattern data by counting a number of times
said force signal exceeds at least one of said plurality of limit
values in a time period between said start time and said end time
determined by said determinator; and
judging device for determining the type of defect on said surface
of said workpiece during finishing, based on results of said
comparative analysis.
2. The apparatus of claim 1 wherein said comparator performs said
comparative analysis on said force signal and said mode pattern
data periodically.
3. The apparatus of claim 1, wherein the mode pattern data are
obtained from an analysis of the force signals generated in trial
cutting processes performed in advance of finishing the
surface.
4. The apparatus of claim 1, wherein
the mode pattern data include reference data to distinguish an
abnormal state of the detector means from a normal state thereof;
and
the judging device judges if the detector falls into the abnormal
state based on the comparative analysis on the force signal and the
reference data.
5. The apparatus of claim 4, wherein
the reference data includes force shift data in the force signal
which occurs when the apparatus stops to finish the surface;
and
judgment of the abnormal state in the detector is based on a
comparison between the force shift data and the force signal.
6. The apparatus of claim 1, further comprising:
a drive means for adjusting setting angles of the cutting tool in a
tool setting step; and
control means for setting the cutting tool to appropriate setting
angles by controlling the driving so as to minimize a fluctuation
ratio, the fluctuation ratio being a ratio of fluctuation of the
force signal divided by an average of the same force signal.
7. The apparatus of claim 1, wherein
the mode pattern data including reference data corresponding to an
abnormal state in lubricating a tip of the cutting tool; and
the judging device finds an occurrence of abnormal state in the
lubrication based on a comparative analysis of the force signal and
the reference data.
8. The apparatus of claim 7, further comprising
a lubricator for controlling the lubrication, which responds to the
finding of the occurrence of the abnormal state by the judging
device.
9. The apparatus of claim 1, wherein
the mode pattern data includes reference data which corresponds to
an abnormal state in chip collection from the workpiece, the
abnormal state in the chip collection including a chip packing and
chip entanglement; and
the judging device judges an occurrence of the abnormal state in
the chip collection.
10. The apparatus of claim 9, further comprising
a lubricator for controlling lubrication of the tip of the cutting
tool responsive to the judgment by the judging device.
11. The apparatus of claim 9, further comprising
a collector for controlling collection of the chips from the
workpiece responsive to the judgment by the judging device.
12. The apparatus of claim 1 wherein said mode pattern data include
mode patterns corresponding to:
(a) a rough workpiece surface caused by vibration,
(b) a rough workpiece surface caused by scratches,
(c) a rubbed surface workpiece surface caused by cutting chips,
and
(d) a surface of said workpiece with an uncut portion.
13. A cutting method for finishing a surface of a workpiece, said
workpiece comprising a metallic material to be used as a substrate
of a photoreceptor in an image forming apparatus, said cutting
method comprising:
storing a plurality of mode pattern data, said mode pattern data
including a plurality of mode patterns, each of which expresses one
of a plurality of types of defects which may occur on a surface of
said workpiece;
cutting said workpiece with a cutting tool;
detecting a cutting force exerted on said cutting tool by said
workpiece with a detector means directly contacting said cutting
tool;
generating a force signal responsive to said cutting force and
changes thereof for a predetermined period of time;
determining a start time and an end time of cutting said workpiece
with said cutting tool according to said cutting force; performing
a comparative analysis on said force signal and said mode pattern
data during the time between the determined start time and the
determined end time; and
determining the type of defect on said surface of said workpiece
during finishing, based on results of said comparative
analysis.
14. The cutting method of claim 13 further comprising;
controlling said cutting tool based on results of said comparative
analysis.
15. The cutting method of claim 13 wherein said mode pattern data
is obtained by;
detection of a cutting force exerted on said cutting tool by said
workpiece; generation of a force signal responsive to a change in
said cutting force for a predetermined period of time;
determination of a maximum peak value of said cutting force;
repeating said detection, said generation and said determination to
obtain a plurality of maximum peak values of said cutting
force;
obtaining an average value and a standard deviation value of said
plurality of maximum peak values, and
obtaining a plurality of limit values according to said average
value and said standard deviation value of said plurality of
maximum peak values.
16. The cutting method of claim 15 wherein said comparative
analysis includes:
counting a number of times a value of said force signal exceeds at
least one of said plurality of limit values between said start time
and said end time.
17. The cutting method of claim 14 comprising counting periodically
a number of times a value of said force signal exceeds at least one
of a plurality of limit values between said start time and said end
time.
18. The cutting method of claim 15 comprising obtaining said
average value and said standard deviation value from said plurality
of maximum peak values excluding a highest value and a lowest value
of said plurality of maximum peak values.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a machine tool which machines a
metallic cylindrical member used for an image forming
apparatus.
In the field of ultra precision machining, for example, in the
field of machining photoreceptor drums or magnetic disk substrates,
mirror-finishing is generally carried out. When products with a
mirror-finish are inspected, not only the dimensional and
configurational accuracy but also the degree of mirror-finishing is
important, so that a very fine flaw such as a scratch, the width of
which is about 10 .mu.m, is not allowed.
When the surface of a product subjected to mirror-finishing is
inspected, visual inspection is conducted at the present time.
Skilled workers are required for visual inspection. Accordingly,
problems are caused when machining is automated.
The following investigations have been carried out on the
inspection of surface conditions.
(1) A technique to measure surface roughness of a workpiece with
scattered light obtained when laser beams are projected on the
surface of the workpiece. ("In-process Roughness Measurement of
Mirror Turned Surfaces by Diffracted Light" by Kenji Morita and
Yoichi Kawakubo; Journal of the JSPE, 1988, 642-646)
(2) A technique to measure and evaluate fine flaws on a machined
surface with scattered light obtained when laser beams are
projected on the surface of a workpiece. ("Measurement of Fine
Scratches by Scattering of Electromagnetic Waves", by Takashi
Miyoshi, Y. Kang, and Katsumasa Saito, Journal of the JSPE, 1988,
1095-1100)
(3) A technique to measure surface roughness under the non-contact
condition by the critical angle method using laser beams. ("Outline
of In-process Measurement and Workpiece-Referred From Accuracy
Control" by Tsuguo Kohno, published in the text book of the
symposium held by the JSPE, 1990, 1-5)
Machining conditions are monitored while consideration is given to
vibrations caused in the process of machining, Acoustic Emission
(AE) signals and heat flow, and the following investigation has
been carried out.
(4) A technique to monitor entangled chips when consideration is
given to heat flux. ("Realization of a machining environment based
on measurement of heat fluxes-Evaluation of appropriateness of the
result of measurement" by H. Nino, M. Rahman, and T. Inaba.
Preprint of the JSPE, September, 1990, 583-584)
(5) A technique to realize wear of cutting tools with ultrasonic
waves ("Realization of wear of cutting tools with an ultrasonic
wave in-process sensor" by S. Itoh, F. Shirasawa, T. Inaba, and Y.
Itoh. Preprint of the JSPE, September, 1990, 585-586)
In order to perform highly accurate machining, the following
attempt has been made. According to the result of measurement of
the configuration of a workpiece, feedback control is conducted so
that a depth of cut can be controlled. ("Outline of In-process
Measurement and Workpiece-Referred From Accuracy Control" by T.
Kohno, published in the text book of the symposium held by the
JSPE, 1990, 1-5)
An object of the conventional technique by which vibrations caused
in the process of machining or AE signals are monitored, is to
detect wear or damage of a cutting tool. In the case of the
conventional technique by which heat flow is monitored, it is
difficult to detect a quickly changing phenomenon, because
information about heat is transmitted with a time delay. The
aforementioned conventional technique is adopted for precision
machining on an ordinary level, so that it is not appropriate for
ultra precision cutting.
An optical measuring method which uses laser beams has the
following drawbacks.
When surface configuration or roughness is optically measured with
laser beams, it is difficult to match the tip of a cutting tool
with a point in which measurement is carried out with a sensor.
Consequently, the sensor can not detect information of the point in
which machining is conducted, so that there is a small difference
between the obtained information and the information of the point
in which machining is being carried out.
A cutting lubricant is used in an actual machining process.
Accordingly, when an optical measuring method is adopted, the
result of measurement is affected by the cutting lubricant.
Therefore, it is difficult to adopt the optical measuring method
for a practical production process. When the optical measuring
process is adopted, the workpiece must be measured after machining,
so that it takes time for inspection.
Therefore, the inventors have taken notice of cutting force
generated in the process of machining. The reason is described as
follows. The cutting force is a physical quantity which is
generated at a point in which machining is carried out.
Accordingly, in accordance with the change of configuration or
roughness of a workpiece surface, the cutting force is changed.
In order to judge a machining state of a workpiece from the data of
cutting force generated in the process of machining, the criteria
has been experimentally found, and in order to reduce the influence
caused by the fluctuation of cutting force, a large allowance is
made in the criteria.
Consequently, the criteria is not appropriate for ultra precision
machining in which the machining state is finely varied.
When a sensor is damaged in the process of machining, damage of the
sensor can not be realized, so that subsequent judgment becomes
inaccurate or impossible.
At present, automatic setting of a monocrystal diamond cutting tool
in the field of ultra precision machining has not yet been
researched and developed. Accordingly, arrangements for a cutting
tool is conducted by a skilled worker. The cutting tool is mounted
on a cutting apparatus by trial and error, so that it takes a long
period of time to arrange the cutting tool, and productivity can
not be improved.
As described before, an optical method with laser beams has been
investigated for the purpose of measuring the state of a surface.
However, this measuring method has not been applied to automatic
setting of a cutting tool.
When the optical measuring method is adopted, it is necessary to
measure a workpiece after a trial machining operation has been
carried out, so that it takes a long period of time for
measurement. Therefore, in order to improve productivity, it is
necessary to reduce measuring time. Further, in practical machining
work, a cutting lubricant is utilized, so that the optical
measuring method is affected by the lubricant oil. Therefore, in
order to improve reliability of measurement, it is necessary to
remove the cutting lubricant from the surface of the workpiece.
The inventors have studied cutting force generated in the process
of machining so that the cutting force can be used as a parameter
during measurement. It has been known that: when the center height
or cutting tool setting angle is slightly changed, the surface
condition of a workpiece is changed in the process of ultra
precision cutting. Machining is a phenomenon carried out in
accordance with the law of dynamics. Accordingly, when the surface
condition is changed, the cutting force is also changed.
In the field of ultra precision cutting, in other words, in the
field of machining a photoreceptor drum base or magnetic disk
substrate, a natural monocrystal diamond cutting tool is utilized
so as to obtain a mirror surface. Even when the cutting tool is set
appropriately, chips are entangled or scratches are caused on the
surface of a workpiece if the cutting lubricant is not supplied
appropriately or chips are not collected properly.
Supply of cutting lubricant and collection of chips are adjusted by
a worker who monitors the conditions of cutting lubricant supply
and chip collection.
At present in the field of ultra precision machining, automatic
adjustment of cutting lubricant supply and chip collection has not
yet been researched and developed. Therefore, in an actual
machining operation, cutting lubricant supply and chip collection
are adjusted by trial and error.
As described before, an optical measuring method with laser beams
has been investigated so as to measure the surface condition of a
workpiece. However, the optical method has not been applied to
adjustment of cutting lubricant supply and chip collection.
When the optical measuring method is adopted, it is necessary to
measure a workpiece after a trial machining operation has been
carried out, so that it takes a long period of time for
measurement. Therefore, in order to improve productivity, it is
necessary to reduce measuring time. Further, in practical machining
work, a cutting lubricant is utilized, so that the optical
measuring method is affected by the lubricant oil. Therefore, in
order to improve reliability of measurement, it is necessary to
remove the cutting lubricant from the surface of the workpiece.
Conventionally, cutting lubricant supply and chip collection are
monitored and adjusted by a worker. Therefore, appropriate actions
can not be taken in time, and a large number of defective products
tend to be successively produced.
Accordingly, cutting lubricant supply and chip collection have an
important effect on the result of machining.
The inventors have studied cutting force generated in the process
of machining so that the cutting force can be used as a parameter
during measurement. It has been known that: when the cutting
lubricant supply condition or chip collecting condition is slightly
changed, the surface condition of a workpiece is changed in the
process of ultra precision cutting. Machining is a phenomenon
carried out in accordance with the law of dynamics. Accordingly,
when the surface condition is changed, the cutting force is also
changed.
When an abnormally strong cutting force is applied to a force
sensor, or when the force sensor collides with an object, the force
sensor is damaged and it is difficult to restore. Accordingly, it
is necessary to provide a protecting device in order to prevent the
force sensor from being deformed beyond a predetermined range.
In general, the protecting device of a force sensor is arranged in
the following manner: a strong block is provided on the external
wall of the force sensor, and the block is provided with a small
gap between the block surface and the outer wall of a cutting tool
rest, wherein the gap can be adjusted by a screw mechanism; and
when a strong force is applied to the force sensor, an abnormally
large deformation of the sensor can be prevented by the block. In
this case, it is necessary to adjust the aforementioned gap in a
range of several microns to several tens microns. Therefore, it is
difficult to adjust the gap so accurately with the screw mechanism.
Accordingly, it takes a large amount of time to adjust the screw
mechanism. That is, it is difficult to prevent the damage of the
force sensor with such a structure as mentioned above.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the
aforementioned problems. It is a primary object of the present
invention to provide a cutting apparatus applied to the field of
ultra precision machining, and the cutting apparatus can detect and
realize the cutting condition and configuration of a workpiece in
real time so that the obtained information can be fed back to the
cutting operation.
Another object of the present invention is to provide a cutting
apparatus applied to the field of ultra precision machining,
wherein a cutting tool can be most appropriately set.
A further object of the present invention is to provide an
adjusting device applied to the field of ultra precision machining,
wherein the adjusting device can adjust the cutting lubricant
supply condition and chip collecting condition to be the most
appropriate.
A further object of the present invention is to provide a cutting
apparatus characterized in that: an available range of a force
sensor is very accurately set, so that damage of the force sensor
can be prevented.
The aforementioned object can be accomplished by a cutting
apparatus by which a metallic thin cylinder for use in an image
forming apparatus is machined, and the cutting apparatus comprises:
a detection means to detect a cutting force generated in a cutting
tool when the workpiece is cut by the cutting tool; a memory means
to store a plurality of mode pattern signals sent from the
aforementioned detection means which are classified according to
the surface condition of the metallic thin cylinder machined with
the cutting apparatus in advance; and a comparison means which
compares an output signal sent from the detection means in the
process of cutting, with the plurality of mode pattern signals
stored in the memory means, wherein the cutting apparatus detects
the cutting condition of the metallic thin cylinder in real time
when the output signal sent in the process of cutting, and the mode
pattern signal which was set previously in accordance with cutting
force data obtained in a trial machining process.
The aforementioned object can be accomplished by a cutting
apparatus to cut a metallic thin cylinder, comprising: a detection
means to detect a cutting force generated in a cutting tool when
the workpiece is cut by the cutting tool; a displacement mechanism
which fixes and displaces the cutting tool when the cutting tool is
set; a memory means to store a plurality of mode pattern signals
sent from the aforementioned detection means which are classified
according to the surface condition of the metallic thin cylinder
machined with the cutting apparatus; and a comparison means which
compares an output signal sent from the detection means in the
process of cutting, with the plurality of mode pattern signals
stored in the memory means, wherein a set angle of the cutting tool
is controlled from the output signal so that a value obtained when
a cutting force fluctuation value is divided by a cutting force
average value, can be minimum.
The aforementioned object can be accomplished by a cutting
apparatus by which a metallic thin cylinder for use in an image
forming apparatus is machined, and the cutting apparatus comprises:
a detection means to detect a cutting force generated in a cutting
tool when the workpiece is cut by the cutting tool; a memory means
to store a plurality of mode pattern signals sent from the
aforementioned detection means which are classified according to
the surface condition of the metallic thin cylinder machined with
the cutting apparatus; and a comparison means which compares an
output signal sent from the detection means in the process of
cutting, with the plurality of mode pattern signals stored in the
memory means, wherein at least one of the cutting lubricant supply
condition with respect to the cutting tool and the chip collecting
condition is automatically detected in real time when the output
sent in the process of cutting is compared with the plurality of
mode pattern signals stored in the memory means by the comparison
means.
The aforementioned object can be accomplished by a cutting
apparatus by which a metallic thin cylinder for use in an image
forming apparatus is machined, and the cutting apparatus comprises:
a force sensor to detect a cutting force generated in the process
of cutting which is provided on a cutting tool rest, wherein an
activating range of the force sensor is regulated with a piezo
electric element to prevent the force sensor from being
damaged.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a cutting apparatus;
FIGS. 2-a, 2-b, 2-c, 2-d to 2-e are views showing output waveforms
of cutting force generated in the process of cutting;
FIG. 3 is a flow chart showing a process to set upper and lower
criteria with which judgment is conducted;
FIGS. 4-a, 4-b to 4-c are views showing the relation between the
variation of cutting force and the drift of output signal.
FIGS. 5-a, 5-b to 5-c are views showing fluctuation of cutting
force generated in the process of cutting;
FIG. 6 is a schematic illustration showing the outline of the
cutting apparatus;
FIG. 7 is a schematic illustration showing an essential portion of
the cutting apparatus;
FIG. 8 is a plan view of an essential portion of the cutting
apparatus;
FIG. 9 is a sectional view taken on line IV--IV in FIG. 8;
FIG. 10 is a view showing waveforms of an output signal of cutting
force corresponding to a normal cutting condition in which a mirror
surface can be obtained;
FIG. 11 is a graph showing a relation between a cutting tool set
angle and a fluctuation and an average of cutting force;
FIG. 12 is a graph showing a relation between a cutting tool set
angle and a fluctuation/average of cutting force;
FIG. 13 is a schematic illustration showing the items of adjustment
of a cutting apparatus;
FIG. 14 is a schematic illustration showing a positional relation
between a cutting tool and a workpiece;
FIG. 15 is a schematic illustration showing the structure of a
cutting apparatus;
FIG. 16-a is a schematic illustration of a cutting lubricant supply
device;
FIG. 16-b is a schematic illustration of an essential portion of
the cutting lubricant supply device;
FIG. 17 is a schematic illustration of an adjusting apparatus for
chip collection hood;
FIG. 18 is a view showing waveforms of an output signal of cutting
force corresponding to a normal cutting condition in which a mirror
surface can be obtained;
FIGS. 19-a, 19-b to 19-c are graphs showing waveforms of output
signals of cutting force corresponding to various cutting
conditions;
FIG. 20 is a schematic illustration of a cutting apparatus;
FIG. 21 is a graph showing a waveform of an output signal of
cutting force; and
FIG. 22 is a view showing the detail of structure of a cutting tool
rest.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the cutting apparatus of the present invention
will be explained as follows. FIGS. 1 to 5 show the first
embodiment. FIG. 1 is a schematic illustration of the cutting
apparatus, and FIGS. 2-a to 2-e are views showing output waveforms
of cutting force.
A cutting apparatus of the present invention is provided to cut a
metallic thin cylinder used for an image forming apparatus. A lathe
2 cuts a photoreceptor drum 1 which is a metallic thin cylinder
member used for a copier or laser beam printer, so that the lathe 2
is provided with a cutting tool rest 3. A force sensor 4 to detect
cutting force is mounted on the tool rest 3. This force sensor 4
composes a detection means to detect cutting force given to cutting
tool A.
An output signal obtained by the force sensor 4 is amplified by a
strain amplifier 5, and converted into a digital signal by an AD
converter 6, and then taken into a computer 7. The computer 7 is
connected with a memory and disk which compose a memory means 8. A
plurality of mode pattern signals stored in the memory being
classified according to the surface condition of a workpiece, and
an output signal obtained by the force sensor 4 are compared by a
comparison means 9 so that the cutting state can be detected. In
the computer 7, a signal to control cutting is made. The control
signal is sent to an NC device to control the lathe 2, or to a
sequence device 10 through a digital IO board and RS232C
interface.
The output signal obtained by the force sensor 4 may be inputted
into the AD converter 6 after filtering has been conducted with a
low-pass filter, high-pass filter and band-pass filter. The
aforementioned filtering may be conducted in the software after the
control signal has been AD-converted by the AD-converter 6, so that
noise can be removed from the signal.
A method of detection of cutting force given to a cutting tool
during a cutting process, is described in "Trial of a Monoblock
Type 3-directional Force Sensor Holder for Disc Substrates of
magnetic memory discs, " by Y Hatamura and M. Adachi. Preprint of
the JSPE, November 1989, 547-548. As described in the thesis, a
cutting force detection holder into which a tool is integrally
incorporated, can be utilized. The size of this holder is the same
as that of a usual holder, so that the holder features a compact
shape and high stiffness. When this holder is put into practical
use, a mirror surface can be formed and the configuration can be
formed as accurately as a common holder, which has been ensured
through an experiment.
For example, strain amplifier DPM613B made by Kyowa Dengyo may be
used for the strain amplifier 5, AD conversion board ADX-98E made
by Canopus Co. is used for the AD converter, IO board PIO-24/24(98)
made by Contec Co. is used for the interface board, and PC-9801UV
made by NEC Co. is used for the computer.
An example will be described as follows in which this cutting
apparatus was used so that the cutting condition was detected. The
photoreceptor drum body 1 made of an aluminum thin cylinder was cut
with the cutting apparatus, wherein the material of the thin
cylinder was A5805, the diameter was 60 mm, and the thickness was 1
mm. A flat cutting tool made of natural mono-crystal diamond was
utilized. The cutting conditions were as follows: the spindle speed
is 6000 rpm, the feed rate is 0.2 mm/rev, and depth of cut is 20
.mu.m.
When the photoreceptor drum body 1 is machined, it is important to
maintain an excellent the surface condition. Specifically, defects
such as vibrations, scratches, entangled chips, and portions which
have not been cut, must be avoided. These defects are
conventionally inspected by a worker by means of visual inspection.
However, it has been found: when patterns of cutting force output
signals are classified, the aforementioned defects can be detected
from the output signals.
When the cutting force is detected, it is checked whether the force
sensor 4 is operated normally or not. Specifically, the check is
conducted as follows. In the force sensor 4, force is converted
into strain with a strain gauge, so that the circuit is balanced
with the strain amplifier 5 before the start of operation. When an
output signal obtained after the circuit has been balanced, is in a
range which has been previously set, it is judged that the force
sensor 4 is in a normal operation. When there is a damage such as a
disconnection in the circuit of the sensor 4, the output signal
obtained after the circuit has been balanced, is out of the
predetermined range, so that it is judged that the force sensor 4
is not in a normal operation.
FIG. 2-a shows an output signal waveform of cutting force
corresponding to a normal cutting condition in which a mirror
surface of 0.2 S to 0.3 S can be obtained. Concurrently with the
start of cutting, the cutting force is detected. When consideration
is given to the rise of the output signal of cutting force, the
start of cutting is automatically judged. The output signal returns
to approximately zero concurrently when the cutting operation has
been completed. Accordingly, when consideration is given to this
fall of the signal, the completion of cutting is automatically
judged.
FIG. 2-b shows a waveform of an output signal in the case where
vibrations have occurred in a workpiece. When vibrations have
occurred, defective vibration marks are formed on the surface of
the workpiece. Vibrations are caused when the cutting force is
increased due to wear of a cutting tool, or when the vibration
proof jig is not sufficient. According to FIG. 2-b, amplitudes of
variation of cutting force are gradually increased as compared with
the waveform of an output signal shown in FIG. 2-a. Accordingly, it
can be said that the vibrations are caused by resonance.
FIG. 2-c shows a waveform of an output in the case where
stripe-shaped scratches, the width of which is several mm, are
caused. The aforementioned scratches are caused in the case where
the cutting force is increased due to wear of a cutting tool so
that burnishing effects become inappropriate. This case features a
pulse-shaped peak of cutting force. According to the results of
observation of the photoreceptor drum body which has been machined,
a scratch is caused in a position coincident with a peak of the
waveform, so that the waveform of the output signal is completely
coincident with the shape of the workpiece.
FIG. 2-d shows a waveform of an output signal in the case where
chips are entangled. Since chips are entangled, the surface of a
workpiece is damaged, so that the workpiece becomes defective. It
can be seen from the drawing that the cutting force is increased in
a position where chips are entangled.
FIG. 2-e shows a waveform of an output signal in the case where all
the surface of a workpiece has not been cut. This case is caused
when a material cylinder for the photoreceptor drum is deformed. In
this case, a mirror surface can not be provided on a portion of the
surface of the drum which has not been cut, so that the drum
becomes defective. As can be seen from the drawing, a level of the
cutting force output signal becomes zero in a portion of the
surface of the drum which has not been cut.
In FIGS. 2-a to 2-e, data sampling frequency is 5 kHz. Some of the
obtained data are omitted on the graphs for simplification.
As described above, there is a correlation between the surface
condition of a workpiece and the output signal of cutting force.
Accordingly, when the patterns of the correlation are previously
stored and the patterns are compared with output signals obtained
while the workpiece is being cut, the cutting conditions can be
detected.
Criteria obtained through trial cutting are incorporated into the
mode patterns of cutting force which are stored in the
aforementioned memory means.
The aforementioned criteria of cutting force are determined
according to the flow chart shown in FIG. 3.
When the trial cutting is carried out, appropriate cutting
conditions are set on the basis of experiences and actual results.
In case a problem is caused in the process of trial cutting,
temporary criteria are set.
The trial cutting is performed 5 times at each cutting force in a
normal cutting condition. The average (F.sub.mean) and standard
deviation (F.sub.sigma) are found from the obtained upper peak
cutting forces in the following manner: the maximum and minimum
cutting forces are excluded from 5 peak values F.sub.max (1),
F.sub.max (2), . . . , F.sub.max (5) which have been obtained in 5
cutting operations, for example, on the assumption that F.sub.max
(2) is maximum and F.sub.max (3) is minimum, the average
(F.sub.mean) and standard deviation (F.sub.sigma) are calculated
from F.sub.max (1), F.sub.max (4) and F.sub.max (5).
As a result, the upper limit (F.sub.upper) of the criteria can be
determined as follows.
In the above equation, .alpha.1 is a proportional constant which is
determined according to experience and know-how.
In the same manner as mentioned above, lower limit (F.sub.lower) of
the criteria is found as follows. The maximum and minimum values
are excluded from lower peak values F.sub.min (1), F.sub.min (2), .
. . , F.sub.min (5). Then, F.sub.mean and F.sub.sigma are found
from the residual 3 values. Lower limit (F.sub.lower) is calculated
from the following equation.
When a cutting force is judged which has been detected with
threshold values of upper limit (F.sub.upper) and lower limit
(F.sub.lower), in the case of normal cutting shown in FIG. 2-a, the
detected cutting force is in the range between the upper and lower
limits.
In the case where vibrations are caused as shown in FIG. 2-b, the
detected cutting forces exceed the upper and lower limits
approximately at the same frequency.
In the case where stripe-shaped scratches are caused as shown in
FIG. 2-c, the detected cutting force exceeds the upper limit of
criteria of cutting force.
In the case where chips are entangled as shown in FIG. 2-d, the
detected cutting forces exceed both the upper and lower limits, and
the frequency to exceed the upper limit is higher than that to
exceed the lower limit. In other words, the average of cutting
force is increased.
In the case where all the surface is not cut as shown in FIG. 2-e,
the detected cutting force exceeds the lower limit of the
criteria.
The aforementioned judgment is conducted according to the following
criteria with regard to consecutive 16 points in the case where
sampling of cutting force is performed at 5 KHz.
For example, when a comparison is made between the frequency at
which cutting force data of 16 consecutive points exceed the upper
limit and the frequency at which cutting force data exceed the
lower limit, the cutting condition can be judged as shown in Table
1. When the number of points which exceed the limits, becomes not
less than 10, it can be judged that the cutting condition is
abnormal.
TABLE 1 ______________________________________ Frequency exceed-
Frequency exceeding Judgment of the ing the upper limit the lower
limit cutting condition ______________________________________ 5 5
Vibrations 6 4 Vibrations 9 1 Scratches 7 3 Entangled chips 0 10
Some portions have not been cut.
______________________________________
The aforementioned frequencies are stored in the memory means, and
compared with the data of cutting force detected in real time so
that the cutting condition of the workpiece can be judged.
FIGS. 4-a to 4-c are graphs showing the relation between the
variation of cutting force and the drift of the output signal. FIG.
4-a shows a normal cutting condition in which the cutting force at
point t after 80% of cutting time (s) has passed, exceeds neither
the upper nor lower limit, and the cutting force after cutting has
been completed, is zero, that is, the drift is zero.
FIG. 4-b is a graph showing a condition in which the cutting force
at point t exceeds the lower limit and the cutting force after the
cutting has been completed, is not more than the zero level due to
the factors such as the increase of temperature. FIG. 4-c is a
graph showing a condition in which the cutting force at point t
exceeds the upper limit, and the cutting force does not return to
the zero level due to the decrease of temperature.
When the deviation from the zero level exceeds an appropriate value
in the cases of FIGS. 4-b and 4-c, it is judged that the cutting
force detection holder is thermally unbalanced and in an abnormal
condition.
When the force sensor 4 which is a cutting force detection means,
is in an abnormal condition, it can be detected as follows.
FIG. 5-a shows a case in which the force sensor 4 is damaged in the
process of cutting. Of course, the detection of cutting force is
interrupted.
When a new force sensor 4, the performance of which is normal, is
installed, the cutting force is varied as shown in FIG. 5-b at the
start of zero balance adjustment. However, right after that, the
cutting force can be detected stably.
Conversely, when the force sensor 4 is abnormal, the cutting force
can not be detected at all as shown in FIG. 5-c even when a zero
balance adjustment is started, so that an abnormal pattern signal
is provided.
According to the present invention, the cutting condition of a
workpiece can be judged according to an objective criteria and
realized in real time. As a result, a highly reliable automatic
ultra precision cutting apparatus can be provided.
With reference to the attached drawings, the second preferred
embodiment of the present invention will be explained as
follows.
FIG. 6 is a schematic illustration of a cutting apparatus of the
second preferred embodiment. A cutting apparatus of the present
invention is provided to cut a metallic thin cylinder used for an
image forming apparatus. A lathe 102 cuts a photoreceptor drum 101
which is a metallic thin cylinder member used for a copier or laser
beam printer, so that the lathe 102 is provided with a cutting tool
rest 103. The cutting tool rest 103 is further provided with a
displacement mechanism 104 which can be controlled with a control
signal sent from the outside of the apparatus to adjust cutting
tool A. A force sensor 105 which detects a cutting force in the
process of cutting, is mounted on the displacement mechanism 104.
This force sensor 105 composes a detection means to detect cutting
force given to cutting tool A. An output signal obtained by the
force sensor 105 is amplified by a strain amplifier 106, and
converted into a digital signal by an AD converter 107, and then
taken into a computer 108. The computer 108 is connected with an IC
memory and disk which compose a memory means 109. A plurality of
mode pattern signals stored in the memory being classified
according to the surface condition of a workpiece, and an output
signal obtained by the force sensor 105 are compared by a
comparison means 110 so that the cutting state can be detected.
After the cutting tool setting condition has been detected, a
control signal is made to adjust the cutting tool setting
condition, and sent to the displacement mechanism 104 through
digital signal interface and RS232C so that the cutting tool
setting condition can be automatically adjusted.
FIG. 7 is a schematic illustration showing the structure of the
cutting apparatus, FIG. 8 is a plan view of an essential portion of
the cutting apparatus, and FIG. 9 is a sectional view taken on line
IV--IV in FIG. 8.
The displacement mechanism 104 of the cutting apparatus is
structured so that it can be adjusted in the three directions of
center height, cutting tool setting angle and depth of cut, which
are indicated in FIGS. 13 and 14.
Since the rolling angle is set to a certain setting value in
accordance with the diameter of a workpiece, it is adjusted in this
embodiment in such a manner that: a spacer 113 is provided below a
cutting tool holder 112 so that the holder 112 is fixed. The
rolling angle can be easily controlled by a signal sent from the
outside of the cutting apparatus when the cutting tool is mounted
on a generally known mechanism in which a rotating support
mechanism and a motor are combined.
With regard to center height direction Z, a Z-axis stage 114 is
utilized, and an X-axis stage 115 which is displaced in cutting
direction X, is fixed onto the Z-axis stage 114. For example, a
Z-axis stage MSDZ-120 made by Miyazawa Co., Ltd. may be used for
the Z-axis stage 114, and an X-axis stage MSD-1-25 made by Miyazawa
Co., Ltd. may be used for the X-axis stage 115.
As shown in FIG. 7, a C-shaped plate 116 including a counter weight
116a on its end, is disposed on the X-axis stage 115, and a tool
angle setting mechanism 117 is disposed on the side of the X-axis
stage 115.
The lower side of a cutting tool holder fixing section 180 is
rotatably supported by a base plate 181 through a bearing 182 as
shown in FIG. 9. A force is given from one end of the cutting tool
holder fixing section 180 by an air cylinder 160, and the other end
is pushed by a linear actuator 146, so that the cutting tool is
displaced. For example, a linear actuator LA-30-10-F made by
Harmonic Drive System Co., Ltd may be used for the linear actuator
146.
The displacement system can be easily realized by not only the
aforementioned mechanism but also a conventional mechanism in which
a straight and a rotary motion mechanism are combined.
After adjustments have been conducted with regard to each
direction, the cutting tool is fixed with air clamp mechanisms 140,
141, and then cutting is performed. When electromagnetic valves
142, 143 are operated by a digital signal sent from the computer
108 through a digital IO board 148 so that each portion is clamped
or unclamped.
The Z-axis stage 114 and X-axis stage 115 are driven by an
exclusive controller 144 and driver 145. These controller 144 and
driver 145 are connected with the computer 108 through, for
example, a RS232C interface.
A linear actuator 146 to adjust tool setting angles is also driven
by an exclusive driver 147. This driver 147 and the computer 108
are connected with a digital signal through a digital IO board
148.
The tool setting angle must be controlled the most accurately as
compared with other adjusting items. Therefore, the inclination of
the mount is measured by two displacement sensors 150, 151 to
detect the tool setting angle, and then feedback control is
conducted. Signals sent from the displacement sensors 150, 151 are
amplified by an amplifier 152, converted into a digital signal by
an A/D converter 107, and taken into the computer 108.
The aforementioned automatic adjusting device is applied to the
cutting apparatus 104 used for the lathe 102 which machines the
drum body 101 for use in a copier and a laser printer.
Detection signals obtained from the force sensor 105 may be
inputted into the A/D converter 107 after they have been filtered
by the low-pass, high-pass and band-pass filters, or after the
detection signals have been A/D-converted, they may be filtered in
the software. In this manner, noises are removed from the detection
signal.
In this embodiment, cutting force is detected with a cutting force
detection holder incorporated into a cutting tool which is
described in page 111 to page 112 of "An attempt of monoblock type
three-component holder for cutting a magnetic disk" by Hiroshi
Hatamura and Mitsuaki Adachi published in the Theses of 1988
Autumnal Convention of Precision Engineering Society. The size of
this holder is the same as that of the holder of a conventional
cutting tool, so that it features a compact shape and high
rigidity. In fact, it has already been checked that a mirror
surface was obtained and an accurate shape was formed with this
holder.
A strain amplifier 6M84 made by NEC San-ei Instruments, Ltd. can be
used for the strain amplifier 106. An A/D converting board
ADA12-8/2(98) made by Contec Co., Ltd. can be used for the A/D
converter 107. An IO board PIO-32/32 made by Contec Co., Ltd. can
be used for the digital interface board. A PC-9801RX2 made by NEC
Co., Ltd. can be used for the computer 108. An AH-416 made by
Keyence Co., Ltd. can be used for the displacement sensors 150,
151.
In order to obtain a mirror surface with the aforementioned cutting
apparatus, an experimental cutting was carried out as described
below.
The experiment was conducted under the following conditions to
detect the cutting force: the revolutional speed of the spindle was
3000 rpm, the feed rate was 0.2 mm/rev, and depth of cut was 15
.mu.m.
FIG. 10 shows a waveform of an output signal of cutting force (a
principal force) corresponding to a normal cutting condition in
which a mirror surface, the surface roughness of which is 0.2 S to
0.3 S, can be obtained. Concurrently when a cutting operation has
started, the cutting force is detected, and it returns to zero
concurrently with the completion of cutting. The sampling frequency
of this waveform data of the output signal of cutting force (the
principal force) is 5 KHz. Some of the obtained data are omitted
for simplification.
FIG. 11 is a graph showing a relation between fluctuation value
F.sub.p-p of cutting force and the tool setting angle, and further
showing a relation between average value F.sub.mean and the tool
setting angle. When the tool setting angle becomes small,
stripe-shaped flaws, the width of which is several mm, are caused
on the cutting surface, so that fluctuation of cutting force is
sharply increased. Accordingly, it is possible to automatically
control the tool setting angle of tool A by feeding back this
phenomenon so that the tool setting angle can be controlled to
obtain a mirror surface.
Results of an example of tool angle setting are shown in Table
2.
TABLE 2 ______________________________________ Initial Number of
Convergent Adjustment Setting Angle Adjustment Angle Error (sec)
(time) (sec) (sec) ______________________________________ 160 2 210
-90 210 1 260 -40 300 5 250 -50 510 7 185 -115 560 8 205 -95
______________________________________
However, according to this method, the following problems are
caused: the tool setting angle is converged upon a value smaller
than the most appropriate value; and even when a mirror surface is
obtained during adjustment, it can not be recognized.
Therefore, the inventors contemplated a value obtained when
fluctuation value F.sub.p-p of cutting force was divided by average
value mean, and they confirmed the following fact: when the tool
setting angle was set in such a manner that the value obtained when
fluctuation value F.sub.p-p of cutting force was divided by average
value F.sub.mean, could be minimum as shown in FIG. 12, a mirror
surface was obtained.
Results of an example of adjustment of tool setting angle are shown
in Table 3. In this example, the adjustment of the setting angle is
made as in the same way as the aforementioned example. In this
example, it could be recognized that the tool setting angle was set
in the mirror surface region, so that the number of adjustment was
reduced to 1/2 and the adjustment error was reduced to 1/2 as
compared with the adjustment method described before. Therefore,
the tool setting angle could be set accurately so that a mirror
surface was provided.
TABLE 3 ______________________________________ Initial Number of
Convergent Adjustment Setting Angle Adjustment Angle Error (sec)
(time) (sec) (sec) ______________________________________ 160 1 260
-40 210 3 21 -90 300 0 300 0 510 2 310 10 560 3 320 -20
______________________________________
According to the present invention, the tool setting angle of a
cutting tool can be automatically adjusted to the most appropriate
value, so that a cutting device to obtain an accurate mirror
surface can be provided.
With reference to the attached drawings, the third example of the
present invention will be explained as follows. FIG. 15 is a
schematic illustration showing the outline of structure of a
cutting apparatus. A cutting apparatus of the present invention is
provided to cut a metallic thin cylinder used for an image forming
apparatus. A lathe 202 cuts a photoreceptor drum 201 which is a
metallic thin cylinder member used for a copier or laser beam
printer, so that the lathe 202 is provided with a cutting tool rest
203. A force sensor 206 is mounted on the tool rest 203, and this
force sensor 206 constitutes a detection means to detect cutting
force of cutting tool A. A detection signal obtained from the force
sensor 206 is amplified by a strain amplifier 207, converted into a
digital signal by an A/D converter 208, and taken into a computer
209. The computer 209 is connected with a memory and disk which
serves as a recording means 210. Signals of a plurality of mode
patterns which are stored in the recording means 210 and classified
according to a cutting lubricant supplying condition and a chip
collecting condition, and an output signal obtained from the force
sensor 206 are compared with each other by a comparison means 211
to detect the cutting lubricant supplying condition and the chip
collecting condition. After the aforementioned cutting lubricant
supplying condition and chip collecting condition have been
detected, a control signal to automatically control the cutting
lubricant supplying condition and the chip collecting condition is
made. The control signal is sent to a cutting lubricant supplying
condition adjusting mechanism 204 and a chip collecting condition
adjusting mechanism 205 through a digital signal RS232C interface,
so that the cutting lubricant supplying condition and the chip
collecting condition are automatically adjusted.
In this embodiment, cutting force is detected with a cutting force
detection holder incorporated into a cutting tool which is
described in "Trial of a Monoblock Type 3-directional Force Sensor
Holder for Disc Substrates of magnetic memory discs." by Y.
Hatamura and M. Adachi. Preprint of the JSPE, November 1989,
547-548. The size of this holder is the same as that of the holder
of a conventional cutting tool, so that it features a compact shape
and high rigidity. In fact, it has already been checked that a
mirror surface was obtained and an accurate shape was formed with
this holder.
A strain amplifier 6M84 made by NEC San-ei Instruments, Ltd. can be
used for the strain amplifier 207. An A/D converting board
ADA12-8/2(98) made by Contec Co., Ltd. can be used for the A/D
converter 208. An IO board PIO-32/32 made by Contec Co., Ltd. can
be used for the digital interface board. A PC-9801RX2 made by NEC
Co., Ltd. can be used for the computer 209.
In this case, a workpiece is a thin cylinder made of aluminum
A5805, the diameter of which was 80 mm and the thickness was 1.5
mm. A flat cutting tool made of natural diamond was used. The
cutting conditions were as follows: the spindle speed was 6000 rpm,
the feed rate was 0.2 mm/rev, and depth of cut was 20 .mu.m. The
rolling angle was set at 13 degrees.
Cutting lubricant was automatically supplied to the aforementioned
cutting tool with the following cutting lubricant supplying device
300.
FIGS. 16a and 16b show the structure of a cutting lubricant
supplying device 300. Cutting lubricant in a tank 301 is
pressurized by compressed air and sprayed with a needle spray gun
302. At this time, an amount of cutting lubricant is adjusted with
one electronic regulator 303, and spraying pressure is regulated
with the other electronic regulator 304, so that an appropriate
amount of cutting lubricant of appropriate pressure is sprayed on
the cutting tool.
FIG. 18 shows a waveform of an output signal of cutting force
(pincipal force) corresponding to a normal cutting state in which a
mirror surface, the surface roughness of which is 0.2 S to 0.3 S,
can be obtained. Concurrently when a cutting operation is started,
a cutting force is detected, and concurrently when the cutting
operation is completed, the cutting force returns to approximately
zero. The sampling frequency of the waveform data of the output
signal of this cutting force (pincipal force) is 5 KHz. Some of the
data are omitted for simplification.
In this case, a drift of output waveforms caused by thermal
influence in the cutting process is not recognized. Accordingly,
the amount of cutting lubricant to be supplied is appropriate, so
that the aforementioned electronic regulators 303, 304 are
maintained in a balanced condition.
FIG. 19-a is a graph showing a condition in which: even after a
cutting operation has been completed, the cutting force is not
returned to zero, and a drift of output waveform occurs due to the
influence of heat generated during the cutting process.
Consequently, it shows that the supply of cutting lubricant to the
aforementioned cutting tool is not sufficient.
In this case, the electronic regulator 303 is automatically
adjusted so that the amount of cutting lubricant can be increased.
Accordingly, the amount of cutting lubricant sprayed from the
needle spray gun 302 is increased so that cooling of the cutting
tool can be facilitated. When necessary, the spraying pressure of
cutting lubricant is adjusted with the electronic regulator 304 so
that it can be increased.
FIG. 19-b is a graph showing a condition in which cutting force
returns to a position higher than zero, that is, a reverse drift of
output wave form occurs. Accordingly, it shows that an excessive
amount of cutting lubricant is supplied.
In this case, the electronic regulator 303 is automatically
adjusted so that the amount of supply of cutting lubricant can be
reduced, and the amount of cutting lubricant sprayed from the
needle spray gun 302 is reduced to prevent supercooling of the
cutting tool. When necessary, the spraying pressure of the
electronic regulator 304 is reduced.
FIG. 19-c is a graph showing a waveform of an output in a condition
in which chips are entangled. In this case, a drift of output
waveform caused by heat generated during the cutting process is not
recognized, and a cutting force having abnormally large amplitudes
is generated.
In this case, only the spraying pressure of the electronic
regulator 304 is increased so that entangled chips are forcibly
removed.
In the case where the cutting condition can not be improved even
when the amount of cutting lubricant and the spraying pressure are
adjusted, the cutting lubricant supplying position and chip
collecting condition are adjusted as follows.
As shown in FIG. 16-b, the position to supply cutting lubricant is
adjusted so that cutting lubricant can be directly sprayed on a
cutting point in the following manner: a linear actuator is moved
in the direction of an arrow mark; a motor is rotated in the
direction of an arrow mark; and a setting angle of the needle spray
gun is adjusted.
As shown in FIG. 17, an adjusting device 400 is adjusted so that
chips can be always effectively collected.
A chip collecting hood inlet 402 including a pair of rotatable
members which can be rotated along the tip portion of a chip
taking-in inlet 401, is connected with an oscillating member 404
which is oscillated around a rotating shaft 403 by a linear
actuator, through a rod 405. When the linear actuator is
controlled, a chip collecting hole of the tip of the chip
collecting hood inlet 402 can be rotated in a direction of an arrow
mark shown in FIG. 17. When a gear mechanism driven by a motor is
provided, the entire device can be rotated in a rolling
direction.
When the direction of the aforementioned chip collecting hood inlet
is adjusted in accordance with the direction of chips generated
from the tip of cutting tool A while the photoreceptor drum body
201 is cut, the chips are effectively collected, and entanglement
of chips can be prevented so that the photoreceptor drum body 1 can
be excellently machined.
According to the present invention, a cutting apparatus can be
provided which is characterized in that: cutting lubricant is
appropriately supplied and chips are effectively collected, so that
an abnormal cutting condition caused by a drift or entanglement of
chips can be eliminated, and a mirror surface can be always
obtained.
The fourth example of the cutting apparatus of this invention will
be explained as follows. FIG. 20 is a schematic illustration of the
cutting apparatus, and FIG. 21 is a graph showing an output
waveform of cutting force.
A cutting apparatus of the present invention is provided to cut a
metallic thin cylinder used for an image forming apparatus. A lathe
502 cuts a photoreceptor drum 501 which is a metallic thin cylinder
member used for a copier or laser beam printer, so that the lathe
502 is provided with a cutting tool rest 503. A force sensor 504 in
which strain gauges are utilized, is mounted on the tool rest 503,
and this force sensor 504 constitutes a detection means to detect
cutting force of cutting tool A.
A detection signal obtained from the force sensor 504 is amplified
by a strain amplifier 505, converted into a digital signal by an
A/D converter 506, and taken into a computer 507. The computer 507
is connected with a memory and disk which serves as a recording
means 508. A plurality of mode pattern signals stored in the memory
being classified according to the surface condition of a workpiece,
and an output signal obtained by the force sensor 504 are compared
by a comparison means 509 so that the cutting state can be
detected. In the computer 507, a signal to control cutting is made
after detection. The control signal is sent to an NC device or a
sequence device 510 to control the lathe 502 through a digital IO
board and RS232C interface.
Detection signals obtained from the force sensor 504 may be
inputted into the A/D converter 506 after they have been filtered
by the low-pass, high-pass and band-pass filters, or after the
detection signals have been A/D-converted by the A/D converter 506,
they may be filtered in the software. In this manner, noises can be
removed from the detection signal.
In this embodiment, cutting force is detected with a cutting force
detection holder incorporated into a cutting tool which is
described in "Trial of a Monoblock Type 3-directional Force Sensor
Holder for Disc Substrates of magnetic memory discs." by Y.
Hatamura and M. Adachi. Preprint of the JSPE, November 1989,
547-548. The size of this sensor is the same as that of the holder
of a conventional cutting tool, so that it features a compact shape
and high rigidity. In fact, it has already been checked that a
mirror surface was obtained and an accurate shape was formed with
this sensor.
A strain amplifier made by Kyowa Dengyo Co., Ltd. may be used for
the strain amplifier 505. An AD conversion board ADX-98E made by
Canopus Co., Ltd. may be used for the AD converter. An IO board
PIO-24/24(98) made by Contec Co., Ltd. may be used for the
interface board. A PC-9801UV made by NEC Co., Ltd. may be used for
the computer.
Next, an example will be described in which a cutting condition was
detected with this cutting apparatus. In this case, a workpiece is
a thin cylinder made of aluminum A5805, the diameter of which was
60 mm and the thickness was 1 mm. A flat cutting tool made of
natural diamond was used. The cutting conditions were as follows:
the spindle speed was 6000 rpm, the feed rate was 0.2 mm/rev, and
depth of cut was 20 .mu.m.
When the photoreceptor drum body 501 is machined, the surface
condition is important. Defects to be prevented are as follows:
vibrations, scratches, entanglement of chips, and portions which
have not been cut. Conventionally, these defects are recognized by
means of visual inspection. However, it has been found that these
defects can be detected when the patterns of output signals of
cutting force are classified.
When cutting force is detected, it is checked whether the force
sensor 504 is in a normal operation or not. Specifically, the check
is performed in the following manner: since the force sensor 504
detects a force by converting the force into a strain with a strain
gauge, the circuit of the strain amplifier 505 is balanced before
the operation; and when an output signal obtained after the
balancing operation is in a predetermined range, it is judged that
the sensor is in a normal operation. In the case where a problem
such as breaking of wire is caused in the circuit of the sensor
504, the output signal obtained after the balancing operation is
out of the predetermined range. Accordingly, it can be judged that
the sensor is not in a normal operation.
FIG. 21 is a graph showing an output signal of cutting force
corresponding to a normal cutting condition in which a mirror
surface, the surface roughness of which is 0.2 S to 0.3 S, is
obtained. Concurrently with the start of cutting, the cutting force
is automatically detected and judged with the rise of the output
signal. The output signal returns to zero concurrently with the
completion of cutting. When the fall of the output signal is
detected, the completion of cutting is automatically judged.
FIG. 22 is a view showing the detail of structure of the tool rest
503. Cutting tool A is provided to the force sensor 04 through a
mount 530. The force sensor 504 is fixed to the tool rest 503.
The force sensor 504 is structured in the following manner: a
square hole 531B penetrates the middle portion of square grooves
531A formed on the upper and lower surface; and strain gauges 531
are stuck on the upper and lower surfaces of the square hole 531B
corresponding to the square groove 531A.
The force sensor 504 detects the cutting force of cutting tool A
which is generated when the photoreceptor drum body 501 is
machined. The detection is conducted in the form of detecting the
tensile or compressive strain acted on the upper or lower surface
of the square hole 531B, and the detected cutting force is
outputted as the aforementioned signal waveform.
A small gap G is formed between the upper and lower sides of the
force sensor 504 and restricting members 532. In this case, the
bottom portion of each restricting member 532 is fixed to the force
sensor 504 in such a manner that the bottom portion is brought into
contact with the force sensor 504.
In each restricting member of the cutting apparatus of the present
invention, a piezoelectric element P is provided inside each square
hole 532B which is connected with a groove 532A. When a voltage
impressed upon piezoelectric element P is varied, gap G is finely
adjusted.
Accordingly, a static load is previously given to the cutting tool
while the output of the force sensor 504 is being detected, and
then the load to be given to the sensor is gradually increased.
Gap G is set so that the force sensor 504 can not be deformed
exceeding a predetermined value within a limit (for example, the
predetermined value is set to be 50% to 70% of a critical strain).
Even when a load given to the cutting tool is increased by
adjusting a voltage impressed upon piezoelectric element P,
deformation of the tool rest 531 is restricted by the restricting
member 532 so that the output from the force sensor 504 is not
increased more than a predetermined value.
When the cutting condition is normal and cutting force of cutting
tool A is in a predetermined range, elastic deformation of the
force sensor 504 is restricted in the range of gap G. Therefore,
cutting is continuously conducted while the force sensor 504 is not
brought into contact with each restricting member 532.
In the case of an abnormal cutting condition or an accident, the
cutting force given to the cutting tool exceeds a predetermined
range, so that a strong force is given to the force sensor 504. In
the aforementioned case, the force sensor 504 is deformed and gap G
becomes zero, so that the force sensor 504 is brought into contact
with the restricting member 532. As a result, the deformation of
the force sensor 504 is restricted by the restricting member 532.
Accordingly, the force sensor 504 is not deformed exceeding a
predetermined value, so that the damage of the force sensor can be
prevented.
The aforementioned example shows a mechanism to prevent the damage
of the force sensor 504 in the direction of a principal force. With
regard to the directions of feed force and radial force, the damage
of the force sensor 504 can be easily prevented in the same
manner.
In the case of a force sensor in which a strain gauge is utilized,
the damage of the sensor can be easily prevented when the present
invention is applied.
According to the present invention, a force sensor integrally
incorporated into a cutting tool can be prevented from a damage
caused by an abnormal cutting condition or an unanticipated
accident. As a result, a cutting apparatus can be provided in which
a cutting force is accurately detected so that a mirror surface can
be always obtained.
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